With the development of the society, the fossil resources have gradually depleted, countries around the world begin working on renewable energy materials, and a new green energy—fuel ethanol, which can be used to replace fossil fuel, has been widespread concern at home and abroad. Because its combustion characteristics are very close to gasoline, fuel ethanol can be used by being blended with gasoline in certain proportion, and can also be used directly as a fuel, greatly reducing harmful gas emissions. Fuel ethanol has a broad development space.
As the world population increase rapidly, in order to ensure food supply, some countries gradually begin to apply policies restricting the production ethanol from food crops, thus producing ethanol from non-food crops will become a trend. Sweet sorghum, for its characteristics such as drought resistance, salt and alkali resistance, high adaptability, and high sugar content of the stem, becomes a preferred candidate of such non-food crops.
There are mainly two ways of liquid- and solid-state fermentations for producing ethanol from sweet sorghum straws. The liquid fermentation is to ferment the juice squeezed from fresh sweet sorghum straws; however, the preservatives added necessarily for juice storage will adverse to the fermentation yeast, and the squeezed solid material will contain a certain amount of residual sugar, both of which will decrease ethanol yield. The solid-state fermentation is to directly ferment crushed sweet sorghum straws, which simplifies the raw material pretreatment, avoids the use of preservatives, and reduces sugar loss, thus fundamentally overcoming the lacks of liquid fermentation.
However, most current solid state fermentation technologies still follow the traditional winemaking process, which is carried out in a fixed fermentation pool or tank, and is operated intermittently, and thus the alcohol is volatile, and the production efficiency is low. Also, the crushed straw material has the characteristics of intertwining, and thus it is difficult to realize the continuous flow, and the uncertainty of its movement also brings monitoring difficulties. Therefore, the top priority in developing the industry of producing fuel ethanol by biomass fermentation is to develop new device, reduce cost and energy consumption, increase ethanol yield, and achieve continuous solid-state fermentation.
It is also a technical difficulty existing in the art to simultaneously achieve continuous ethanol separation during the procedure of continuous solid-state fermentation. Because of the high mutual friction force of crushed straw fermentation materials of such as sweet sorghum, sugar cane, they are easy to tear and cake when moving, so it is difficult to realize continuous flowing, which together the characteristics of variability of its movement and the uneasy of detecting motion parameters make it a world difficulty to realize the continuous alcohol steaming using solid state fermentation materials. Therefore, the top priority in realizing the operation of continuous alcohol steaming during straw solid-state fermentation is to achieve the continuity of the alcohol steaming process using solid-state fermentation materials, to increase the concentration and stability of alcohol in gas phase, to improve production efficiency, and to reduce production cost and energy consumption.
In the Chinese patent application publication CN 102094045A, the inventors of the present invention disclosed a device and process for continuously separating ethanol from solid-state fermentation materials, the process comprising the following steps:
(a) The solid-state fermentation materials are fed into the inlet of the continuous alcohol steaming device by a screw conveyor for feeding; the materials uniformly distribute in the rotary grid on the surface of the uppermost heating disk by a distributor; in the heating disk is input with saturated steam of 0.1-1 MPa; and after be heated by the heating disk indirectly, the fermentation materials fall from its material outlet into the corresponding rotary grid on the heating disk of the next layer, continuously and orderly flow towards the outlet of the device, and discharge from a discharging outlet finally;
(b) After heating, the ethanol and water in fermentation materials partially vaporize into distillation gas, which discharges from a top vent, and directly enters into a rectifying tower for rectifying.
Alternatively, the saturated steam in the step (a) is replaced by thermally conductive high temperature oil steam or another hot gas.
Alternatively, the temperature in the continuous alcohol steaming device is kept at 100° C. or above.
The device for continuously separating ethanol from solid-state fermentation materials disclosed in the Chinese patent application publication CN 102094045A comprises a housing, a screw material feeder connecting with the inlet of the housing, a discharging bin connecting with the outlet of the housing and a screw material discharger, a spindle locating on the center axis of the housing and a driving motor connecting with the rotation shaft. Under the screw material feeder, the inner wall of the housing is provided with distributing plate grids, and plurality of heating disks connect in series with the rotation shaft; the heating disk is a hollow body made up by two plates and a side wall, the hollow body in the chamber is provided with steam folding baffles, and is input with water vapor; the heating disks on the sidewall is symmetrically provided with a steam inlet and a steam outlet, and the heating disk is provided with several fan-shaped holes for fermentation materials flowing; each of the heating disks is provided with a rotary grid; each of the steam outlets of the heating disks are connected with the main line of outflow steam via a square pipe, and the main line of outflow steam at the end is provided with a gas-liquid separator, to separate steam and condensate; the housing on the top is provided with a steam outlet, a condenser and a backflow tube which connects the condenser and the screw material feeder.
The heating disk is air-tightly sealed, and the steam can only flow in or out from the inlet and outlet on the heating disk; the feeding inlet and discharging outlet of the housing are both equipped with sealing apparatus, wherein the feeding inlet is sealed by fermentation material accumulation, and the discharging outlet is sealed with a gate valve or a flap valve or a multilayer flap valve, thus the entire device being air-tightly sealed.
The fan-shaped holes on the heating disk in the vertical direction successively shift a distance of the size of the fan-shaped hole opposite to the rotation direction of the rotary grid.
The temperature is kept via using thermal insulating materials on the outside wall of the housing, inputting steam into a jacket or using an electric heating zone, and the temperature is kept at 100° C. or above.
The distributing plate grid is a distributor consisting of several pieces of grid plates, and the fermentation materials inputted by the screw material feeder, after being distributed by the distributor, will be uniformly distributed in the rotary grid on the surface of the heating disk.
The rotary grid is made up by two cylinder plate grids connected via several of straight plate grids, the center of the rotary grid are fixed on the rotation shaft which goes throughout the center of each of the heating discs, and rotary grid rotates along with the rotation shaft.
However, the above device and process for continuously separating ethanol still have some defects, such as: 1. During the distillation procedure, the heating disks are used to heat the materials, and thus the heat transfer efficiency is not ideal; 2. The feeding inlet and discharging outlet have poor air-tight effect, and this makes the outflow of the distillation products; 3. The material thickness in the distillation tower is uneven, and this affects the distillation efficiency; 4. The moisture content of the distillated materials (residues) is high, and they cannot be reused and can only be discharged as industrial waste, which has an evil impact on the environment, etc.
Therefore, there remains a need in the art to achieve a device and process for continuously separating ethanol, so as to solve the problems of low ethanol production rate the difficulty in achieving continuity, and the serious environmental pollution during the current process of producing ethanol from the sweet sorghum straw.